We are investigating gene regulation in early mammalian development using the synthesis of the zona pellucida and proteoglycans as model systems. Using a murine follicle culture we have demonstrated the in vitro biosynthesis of the zona and calculated its turnover and rate of synthesis. The three sulfate containing glycoproteins of the zona have marked size and charge heterogeneity. Pre-incubation with tunicamycin inhibits the secretion of the zona proteins although their intracellular presence can be demonstrated by immunoprecipitation with antizona antibodies. The synthesis of zona proteins terminates with oocyte maturation prior to ovulation. Proteoglycans, however, are not produced during oogenesis and their synthesis begins only in the early embryo. Using our follicle culture we have demonstrated that although intact proteoglycans are synthesized in the surrounding granulosa cells, no proteoglycan or glycoside transferase activity is present either during cogenesis or in superovulated eggs. We have initiated studies to isolate intact proteoglycans from the zygote, the morulae and the early blastocyst stages of the mouse embryo. These macromolecules will be analyzed both as to their composition, biosynthesis and revelant biological role in pre-implantation development.